Clone Graph

Description

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors. How we serialize an undirected graph:

Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbor of the node.

As an example, consider the serialized graph {0,1,2#1,2#2,2}. 
The graph has a total of three nodes, and therefore contains three parts as separated by #.  

First node is labeled as 0. Connect node 0 to both nodes 1 and 2.

Second node is labeled as 1. Connect node 1 to node 2.

Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.

Visually, the graph looks like the following:
   1
  / \
 /   \
0 --- 2
     / \
     \_/

Example
return a deep copied graph.

Link

Lintcode_ladder

Method

1. Use hashmap + vector, search + copy + connect
2. Use hashmap + vector, search/copy + connect
3. Use hashmap, search + copy + connect

Example

1. 1

/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:
    /**
     * @param node: A undirected graph node
     * @return: A undirected graph node
     */
// -------------------------------------------------------------------------
// Version 1. 102ms use the hashmap and vector to solve the problem
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        // write your code here
        if (!node) {
            return nullptr;
        }
        vector<UndirectedGraphNode*> nodes;
        unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> map;
        // find all nodes
        nodes = nodeSearch(node);
        // deep copy all nodes
        int len = nodes.size();
        for (int i = 0; i < len; ++i) {
            map[nodes[i]] = new UndirectedGraphNode(nodes[i]->label);
        }
        // connect new nodes
        for (int i = 0; i < len; ++i) {
            vector<UndirectedGraphNode*>& oldcons = nodes[i]->neighbors;
            vector<UndirectedGraphNode*>& newcons = map[nodes[i]]->neighbors;
            int nlen = oldcons.size();
            newcons.resize(nlen);
            for (int j = 0; j < nlen; ++j) {
                newcons[j] = map[oldcons[j]];
            }
        }
        return map[node];
    }
// modularization/modularize func  
    // bfs : find all unique nodes
    vector<UndirectedGraphNode*> nodeSearch(UndirectedGraphNode* head) {
        vector<UndirectedGraphNode*> result;
        queue<UndirectedGraphNode*> q;
        unordered_set<UndirectedGraphNode*> hset;
        q.push(head);
        hset.insert(head);
        while (!q.empty()) {
            UndirectedGraphNode* cur = q.front();
            q.pop();
            int len = cur->neighbors.size();
            for (int i = 0; i < len; ++i) {
                if (hset.find(cur->neighbors[i]) != hset.end()) {
                    continue;
                }
                hset.insert(cur->neighbors[i]);
                q.push(cur->neighbors[i]);
            }
        }
        // for (auto i = hset.begin(); i != hset.end(); ++i) {
        //     result.push_back(*i);   
        // }
        for (auto& i : hset) {
            result.push_back(i);   
        }
        return result;
    }
// ------------------------------------------------------------------------
// // Version 2, 85ms, All in one
    UndirectedGraphNode* cloneGraph(UndirectedGraphNode* head) {
        if (!head) {
            return nullptr;
        }
        unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> map;
        // search & copy
        UndirectedGraphNode* cur = nullptr;
        queue<UndirectedGraphNode*> q;
        q.push(head);
        map[head] = new UndirectedGraphNode(head->label);
        while (!q.empty()) {
            cur = q.front();
            q.pop();
            // if (!cur) {
            //     continue;
            // }
            int len = cur->neighbors.size();
            for (int i = 0; i < len; ++i) {
                if (cur->neighbors[i] && map.find(cur->neighbors[i]) == map.end()) {
                    q.push(cur->neighbors[i]);
                    map[cur->neighbors[i]] = new UndirectedGraphNode(cur->neighbors[i]->label);
                }
            }
        }
        // connect
        for (auto& cur : map) {
            UndirectedGraphNode* newconn = nullptr;
            int len = cur.first->neighbors.size();
            cur.second->neighbors.resize(len);
            for (int i = 0; i < len; ++i) {
                newconn = map.find(cur.first->neighbors[i])->second;
                cur.second->neighbors[i] = newconn;
            }
        }
        return map.find(head)->second;
    }
// -------------------------------------------------------------------------
// // Version 3, 82ms, trans the ref of hashmap to the whole problem
UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (!node) {
            return nullptr;
        }
        unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> dict;
        // vector<UndirectedGraphNode*> nodes;
        findnodes(dict, node);
        copynodes(dict);
        connectnodes(dict);
        return dict[node];
    }
    void findnodes(unordered_map<UndirectedGraphNode*, UndirectedGraphNode*>& dict, UndirectedGraphNode* node) {
        queue<UndirectedGraphNode*> q;
        q.push(node);
        dict[node] = nullptr;
        while (!q.empty()) {
            auto cur = q.front();
            q.pop();
            // if (dict.find(cur) != dict.end()) {
            //     continue;
            // }
            for (auto& neighbor : cur->neighbors) {
                if (neighbor && dict.find(neighbor) != dict.end()) {
                    continue;
                }
                q.push(neighbor);
                dict[neighbor] = nullptr;
            }
        }
        return;
    }
    // copy all unique nodes
    void copynodes(unordered_map<UndirectedGraphNode*, UndirectedGraphNode*>& dict) {
        for (auto& nodepair : dict) {
            if (!nodepair.second) {
                nodepair.second = new UndirectedGraphNode(nodepair.first->label);
            }
            for (auto& neighbor : nodepair.first->neighbors) {
                if (!dict[neighbor]) {
                    dict[neighbor] = new UndirectedGraphNode(neighbor->label);
                }
            }
        }
        return;
    }
    // connect all unique nodes
    void connectnodes(unordered_map<UndirectedGraphNode*, UndirectedGraphNode*>& dict) {
        for (auto& nodepair : dict) {
            vector<UndirectedGraphNode*>& oldneighbors = nodepair.first->neighbors;
            vector<UndirectedGraphNode*>& newneighbors = nodepair.second->neighbors;
            for (auto& neighbor : oldneighbors) {
                newneighbors.push_back(dict[neighbor]);
            }
        }
        return;
    }
};

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